CO2 is termed a “Natural Refrigerant” because it exists in the natural environment. Release into the atmosphere from refrigeration systems has a negligible effect compared to other CO2 sources that are driving the global warming debate. As a refrigerant, it is a manufactured product that conforms to strict purity specifications. Its physical properties require special handling. The system pressures are much higher than in conventional systems, and all the components are designed accordingly. Today there is no difficulty in sourcing all the necessary equipment. High investment costs were characteristic of early CO2 projects, but these costs are now on a downward trend. The refrigerant itself is a fraction of the cost of some of the specialty HFCs. This handbook reviews the main CO2 properties, explores the advantages of CO2 as a refrigerant, and provides an understanding of system types and their design. This is followed by a study of optimization, operation and maintenance topics. This information will be useful to engineers responsible for designing and maintaining commercial refrigeration systems who are now encountering CO2 systems, perhaps for the first time …